The present invention relates to the field of electronic design and test, and specifically to the field of Computer Aided Engineering (xe2x80x9cCAExe2x80x9d) tools.
Background: Mixed-Signal Devices
Mixed-signal devices require synchronized analog and digital signals to be sourced to the Device-Under-Test (xe2x80x9cDUTxe2x80x9d) for comprehensive test coverage. These mixed analog and digital signals are known as mixed-signal test stimuli. During the design process, a simulated mixed-signal stimulus is developed and sourced to a software model of the DUT. The DUT model""s simulated response to this stimulus is compared against the expected response to verify the quality of the DUT""s design before a physical DUT is manufactured. For years, software CAE tools have existed that can convert digital test signals into a format compatible with Automated Test Equipment (xe2x80x9cATExe2x80x9d). The digital test signals, called digital patterns, consist of one or more digital vectors. Each digital vector is a set of forced and/or expected ones and zeros that are applied to the DUT at a particular point in time during the execution of the digital pattern. Although there are many software tools that can capture and convert digital patterns to an ATE-compatible format, no CAE tool is available today that can perform a similar function on the analog AC and DC signals of a mixed-signal test stimulus. Therefore, the mixed-signal portion of the test program is generated by a test engineer, who uses mostly manual processes to create and measure sine waves, current, DC voltages, and digital patterns that work in combination with these analog signals to exercise the mixed-signal portions of the DUT. Consequently, generation of mixed-signal test programs is still a laborious and manual process.
Background: Traditional CAE Tools
Traditional CAE tools offer a method to convert digital signals from a design simulation test bench format to an ATE-acceptable format. The digital stimulus used on a DUT is created during the design phase of the DUT, and is converted for use during the testing of the DUT with the ATE.
In the prior-art design-to-test process, the designer typically verifies a design using software simulation tools. The digital patterns used to verify the design can be reused to generate a digital test program. Software tools are available from a number of vendors which allow the conversion of designer-generated digital vectors to an ATE-compatible format. However, in prior-art program generation methods there is no way to automatically convert mixed-signal test stimuli from the design environment directly to the test environment. The prior-art process including applying a modulated analog signal to a DUT is set forth in Benoit Dufort and Gordon W. Roberts, Signal Generation Using Periodic Single and Multi-bit Sigma-delta Modulated Streams, 1997 PROC. IEEE INTERNATIONAL TEST CONFERENCE 396-405; Xavier Haurie and Gordon W. Roberts, Arbitraryxe2x80x94Precision Signal generation for Bandlimited Mixed-Signal Testing, 1995 PROC. IEEE INTERNATIONAL TEST CONFERENCE 78-86; and a related copending application entitled xe2x80x9cMethod and Apparatus to Generate Mixed Signal Test Stimulusxe2x80x9d Ser. No. 60/057,271, filed Aug. 28, 1997 all of which are hereby incorporated by reference.
Capture and Conversion of Mixed-Signal Test Stimuli
The present application discloses a method which allows the capture and conversion of mixed-signal stimuli from design test bench generated signals to an ATE-compatible format. The disclosed method makes use of commercially available CAE tools. The invention advantageously uses a xe2x80x9csoftware-generated stimulus modulator (or xe2x80x9cStiModulatorxe2x80x9d) based upon sigma-delta modulation/demodulation technology to allow conversion of digitally simulated analog test signals into digital pattern representations.
The invention takes advantage of prior-art methods (where a designer creates a test circuit for a DUT during the design process, and applies mixed-signal stimuli to that DUT by sourcing simulated digital, AC, and DC signals), by simply processing the digitally simulated analog signals through the StiModulator for storage into a CAE digital pattern file. These digital representations can then be converted to a format compatible with the target tester using existing digital pattern conversion tools.
The StiModulator produces a series of one-bit samples which are applied to a software model of a one-bit digital-to-analog converter (DAC) followed by a low-pass or band-pass reconstruction filter. The filter produces a digital representation of a reconstructed analog signal substantially equal to the digitally simulated source signal. The one-bit samples may also be converted to an ATE-format using the same software CAE tools commercially available for converting digital signal patterns for the DUT. The converted samples are applied to the DUT using ATE digital pin card drivers in the case of digital stimuli, and using pin card drivers in conjunction with reconstruction filters for analog stimuli.